Transcript Calibration of TRMM Precipitation Radar

Calibration of TRMM
Precipitation Radar
Toshio Iguchi
National Institute of Information and
Communications Technology
[email protected]
Achieving Satellite Instrument Calibration for Climate Change
16-18 May 2006
National Conference Center (NCC), Lansdowne, Virginia
TRMM’s Mission Objectives
• To advance the understanding of global circulation of
energy and water from observation of tropical and
subtropical rain
– Accurate measurement of tropical rain which affects the global
climate
• monthly rain accumulation estimates in 5 deg by 5 deg
boxes with less than 10% error (Sampling & Retrieval
error)
– Estimation of vertical distribution of latent heat
• PR provides information on vertical rain profiles
Tropical Rainfall Measuring Mission: TRMM
Solar paddle
High-gain antenna
TMI
VIRS
LIS
PR
Observation of tropical
rainfall (Driving engine
of global atmosphere)
US-Japan joint mission
(Japan: PR, Launch,
US: Bus, 4 sensors,
operation)
CERES
Launched in Nov., 1997.
Still under operation
Orbit
Altitude
Inclination
Circular（Non-Sun Synchronous）
350km (402.5km since Aug. 2001) (±1.25km)
35 deg.
Sensor
Precipitation Radar (PR)
TRMM Microwave Imager (TMI)
Visible and Infrared Scanner (VIRS)
Clouds and the Earth’s Radiation Energy System (CERES)
Lightning (LIS)
First space-borne
precipitation radar
developed by CRL and
NASDA
Concept of TRMM Rain Observation
Flight
Speed:
7.3 km/sec
飛行速度:
7.3 km/sec
PR: 降雨レーダ
PR:
Radar
TMI:Precipitation
TRMMマイクロ波観測装置
TMI: TRMM Microwave Imager
VIRS: 可視赤外観測装置
VIRS: Visible/IR Scanner
PR
VIRS
TMI
250 m
760 km
215 km
720 km
6～50km
4km
2km
Mission Requirements of TRMM PR
・Sensitivity：< 0.７mm/h
・Dynamic range：> 70dB
・Horizontal resolution：< ５km
・Range resolution：< 250ｍ
・Number of independent samples：> 64
（SD of fading noise ＜ 0.7 dB）
・Swath width：> 200km
・Observable range：Surface to 15km
Major Parameters of TRMM PR
Radar type
Antenna type
Beam scanning
Frequency
Polarization
TX/RX pulse width
RX band width
Pulse rep. freq.
Data rate
Mass
Life time
TX peak power
Antenna gain
Beam width
Min det. lv.
Min detectable RR
Power cons.
Pulse radar
128-elem. WG slot array
Active phased array
13.796, 13.802 GHz
Horizontal
1.57 / 1.67 msec
0.6 MHz
2776 Hz
93.5 kbps
460 kg
3 years
> 500 W (708 W)
> 47.4 dB (47.5 dB)
0.71±0.02 deg ( 0.71 deg)
< -110 dBm (-110.3 dBm)
< 0.7 mm/h (0.48 mm/h)
< 250 W (215 W)
All numbers are designed values. The numbers in parentheses are the measured values with the PFM.
Flow of Rain Profile Estimation
Hardware Calibration
• Received Power (Pr)
• Conversion of Pr to Zm (Apparent measured radar reflectivity
factor) using calibration factor of PR
– Pr →Zm
Retrieval Algorithm
• Correction of attenuation due to CLW, WV, and O2
– Zm→Zm'
• Correction of attenuation due to precipitating particles (rain att.
correction assuming k-Ze relation (DSD))
– Zm'→Ze
• Conversion of Ze to R (rain rate)
– Ze→R
Assumptions: distribution of CLW as a function of R, distribution of WV,
type of precipitating particles as a function of height, DSD model,
homogeneity of rain distribution within an IFOV, vertical profile of rain
in surface cluttered range, stable surface scattering cross sections
Radar Equation
where
Ze: effective radar reflectivity factor,
Zm: apparent measured radar reflectivity factor
Pr: received power --- internal & external cal.
Pt: TX power ------------ power monitor (and external cal.)
Gt0: TX antenna gain --- (external cal.)
Gr0: RX antenna gain --- (external cal.)
qt1, qt2, qr1, qr2: Tx and Rx antenna beam width (along and across track) --- (external cal.)
r: range, t: pulse width, c: speed of light,
er: relative dielectric constant, n: refractive index
l: wavelength, k: specific attenuation
Hardware Calibration
• Calibrate the parameters in radar equation:
– Pt: Tx power of SSPA monitored
– Gt: Antenna gain for Tx, external cal.
• qt: beam width, external cal
– Gr: Antenna gain for Rx, external cal.
• qr: beam width, external cal
– Pr: Received power
• LNA cal, internal cal
– Overall calibration: external cal.
• Monitor the stability
–
–
–
–
–
–
Temperatures at various places: Antenna panel, Panel, FCIF
Power Supply Voltage
SSPA Output Power
System Noise
Terminated Log-Amplifier Output
Echoes from natural targets such as ocean surface
TRMM PR Block Diagram (including redundancy
units)
PHS
HYB
SSPA
antenna
SSPA
PHS
LNA
128 elements
antenna
SSPA
PHS
TDA
FCIF
SCDP
FCIF
SCDP
TDA
DIV/COMB
LNA
HYB
antenna
BPF RDA
BPF RDA
LNA
SSPA:
LNA:
PHS:
DIV/COMB:
HYB:
TDA:
RDA:
FCIF:
SCDP:
Solid State Power Amplifier
Low Noise Amplifier
Phase Shifter
Divider/Combiner
Hybrid
Transmitter Drive Amplifier
Receiver Drive Amplifier
Frequency Converter and IF
System Control Data Processor
Housekeeping Records of TRMM PR(1/2)
antenna
SSPA
(3) FCIF Temperature
PHS
DIV/COMB
LNA
TDA
FCIF
SCDP
RDA
(4) Power Supply Voltage
Power Supply
(1) Antenna Panel
Temperature
(2) Panel Temperature
Housekeeping Records of TRMM PR(2/2)
(5) SSPA Output Power Monitor
at each Element
SSPA
LNA
128 elements
PHS
DIV/COMB
antenna
(7) Terminated Log-Amplifier
Output
TDA
FCIF
SCDP
RDA
(6) System Noise at each Angle Bin
[phase code at PHS is varied for all angle bins]
Analysis Procedure of Housekeeping Records
Housekeeping records of TRMM PR are included in two types of telemetry,
HK telemetry and Science telemetry. Their update rate is frequent.
In this analysis, some samples are collected approximately every 2 hours,
and averaged in monthly. Four statistical values, average, standard
deviation, minimum and maximum, are shown in the following plots.
Table 1 Type and Update time of Housekeeping Records
Name
Type
Update time
HK
telemetry
Realtime: 1 sec or 128 sec
Playback: 10 sec
Science
telemetry
1 scan ( 0.6 sec)
(1) Antenna Panel Temperature
(2) Panel Temperature
(3) FCIF Temperature
(4) Power Supply Voltage
(5) SSPA Output Power Monitor
(6) System Noise
(7) Terminated Log-Amplifier Output
(1) Antenna Panel Temperature
350km altitude
400km altitude
Leonide Storm (mid-November)
GSAGE/Sun Acquisition anomaly on 1999-003
Summary of trends in housekeeping records
Name
(1) Antenna Panel Temperature
status
(3) FCIF Temperature
All PR temperatures have remained within limits, even
during planned events like Deep Space Calibration
and the Leonoid storm and anomalies like Low Power
and Sun acquisition.
(4) Power Supply Voltage
Power Supply Voltage have remained within limits.
(5) SSPA Output Power Monitor
All SSPAs work well, and their output powers are fairly
stable except SSPA #011, #106.
A steep change of SSPA #056 at Sep. 2000, a gradual
decrease of SSPA #102 around May 2003 occurred, but
now both SSPAs work stable.
(6) System Noise
Digital Counts have remained within limits.
(7) Terminated Log-Amplifier Output
Digital Counts have remained within limits.
(2) Panel Temperature
The effect of TRMM’s altitude change, from 350 km to 400 km, does not appear in
any housekeeping records variations.
TRMM PR Internal Calibration
Internal Calibration of FCIF & SCDP
(with Transmit Power Off above
Australia, every 3 days)
SSPA
LNA
PHS
DIV/COMB
antenna
TDA
FCIF
SCDP
RDA
Operation Analysis Mode
measures the gain of each Rx channel by
transmitting pulses with all 128 SSPA and
receiving the echoes with only one LNA.
Input-Output Characteristics of
PR Receiver FCIF Unit
出力カウント値
count value
Output
250
200
150
● On-orbit
軌道上測 定結果
●
measurement
■
results
■ PFT
結果
地上試験
100
測定値の
軌道上
Linear
fit of
on-orbit data
直線フィット
50
0
-100
-80
-60
-40
-20
RX input level (dBm)
(dBm)
受信機IF部入力レベル
0
Transmit Antenna Aperture Power Distribution
in Cross-track Direction
送信電力
(dBm)
(dBm)
power
Transmit
45
40
35
On-orbit
measurement
30
Specification
25
Note: SSPA power monitor telemetry is used.
20
0
32
64
SSPA番号
SSPA
Number
96
128
Receive Antenna Aperture Power Distribution
in Cross-track Direction
相対利得
(dB)
(dB)
gain
Relative
5
0
-5
On-orbit
measurement
-10
Specification
-15
Note: Sea surface echo level with activating each LNA is used.
-20
0
32
64
番号
LNALNA
Number
96
128
External Calibration with Active Radar Calibrator
The ARC has tree functions :
・Radar transponder (Transponder mode)
--- over all TX/RX system
・Radar receiver (RX mode)
--- PR TX power, antenna pattern,
PR
PR TX antenna gain
・Beacon transmitter (TX mode)
--- PR RX gain, antenna pattern
ARC
Receiver
PR
ARC
Transmitter
(for PR TX) (for PR RX)
PR
ARC
Delay
Transponder
(for TX/RX total)
Tx Antenna pattern
(PR/TX―ARC/RX)
-30.0
-35.0
PR TX Power ( dBm )
-40.0
-45.0
-50.0
0.735 deg
28.2dB
-55.0
-60.0
-65.0
-70.0
-75.0
-80.0
-3.0
-2.0
-1.0
y = -22.663x2 - 2.4646x - 37.28
R2 = 0.9964
0.0
Angle( degree )
1.0
2.0
3.0
Rx Antenna pattern
(PR/RX―ARC/TX)
-90.0
PR RX Power (dBm)
-95.0
0.717 deg
-100.0
-105.0
-110.0
-115.0
-120.0
-3.0
-2.0
-1.0
0.0
Angle (degree)
1.0
2.0
3.0
Along-track PR Receive Antenna Pattern
Gain (dB)
Relative
相対利得（dB）
0
After Launch
打上げ後
Before Launch
打上げ前
-10
-20
-30
-40
-50
-60
-6
-4
2
0
-2
角度（度）
Angle
(deg)
4
6
Trend of PR Receiver Performance
2.0
2.0
Ver.３
Ver.４
Ver.５
Ver.６
1.0
0.0
0.0
-1.0
orbit change
(measured value)
- (calculated value) (dB)
（実測値）－（計算値）（dB）
Trend
of ARC送信モード／PR受信電力評価のトレンド（1997/12/15～2005/12/10）
Rx power with ARC used as a transmitter
図Ⅳ－13
-2.0
-2.0
97/11 98/05 98/11 99/05 99/11 00/05 00/10 01/04 01/10 02/04 02/10 03/04 03/10 04/04 04/10 05/04 05/10
観測日（UT)
Measurement date (year/month)
Trend図Ⅳ－14
of Tx ARC折返しモード／ARC受信電力評価のトレンド（1998/1/12～2005/12/09)
power of PR with ARC used as a receiver
2.0
2.0
Ver.３
Ver.４
Ver.５
Ver.６
1.0
f2 is used for
comparison
0.0
0.0
-1.0
orbit change
(measured value)
- (calculated value) (dB)
（計算値）－（実測値）（dB）
Trend of PR Transmitter Performance
-2.0
-2.0
97/11 98/05 98/11 99/05 99/11 00/05 00/10 01/04 01/10 02/04 02/10 03/04 03/10 04/04 04/10 05/04 05/10
観測日（UT）
Measurement date (year/month)
ARC折り返しモード／PR受信電力評価のトレンド（1998/1/12～2005/12/09）
Trend図Ⅳ－15
of overall
PR gain with ARC used as a transponder
3.0
3.0
2.0
Ver.３
Ver.４
Ver.５
f2 is used for
comparison
Ver.６
1.0
0.0
0.0
-1.0
-2.0
orbit change
(measured value)
- (calculated value) (dB)
（実測値）－（計算値）（dB）
Trend of PR Overall Gain
-3.0
-3.0
97/11 98/05 98/11 99/05 99/11 00/05 00/10 01/04 01/10 02/04 02/10 03/04 03/10 04/04 04/10 05/04 05/10
観測日（UT）
Measurement date (year/month)
Incidence Angle Dependence of Ocean
Sigma-0 Measured by TRMM PR
radar cross-section(dB)
(dB)
Norm’d
規格化レーダ断面積
16
海面 無降雨, 2/14～3/6 1998,
海面、無降雨、
2/14～3/6
1998、18軌道
No rain cases, 18
orbits
in Feb
14 - Mar. 6, 1998
18 軌道
12
8
ARMAR
ARMAR
CAMPR
CAMPR
4
0
-4
-8
0
2
4
6
8
10
12
14
16
入射角
(度)(deg)
Incidence
Angle
18
20
Monthly variations of sea surface echoes
Variation of normalized sea surface radar cross section
(no-rain cases)
Variability of sea surface echoes
[dB]
Standard Deviation of Monthly Averaged NRCS
(Jan. 1998 - Dec. 2000)
0.14
0.12
0.1
0.08
0.06
0.04
0.02
0
0.1 2.25 4.45 6.75 8.95 11.2 13.5 15.7
Incidence Angle [deg]
18
Global Distribution of the Mean Storm Height Measured
by the TRMM Precipitation Radar
July 1998
January 1999
Tropical Rainfall Anomalies
(TRMM Ocean Retrievals)
V5
BB Height and Freezing Level
(170E-230E)
10S-10N
20S-20N
30S-30N
Brightband Height
Freezing Level (3A11)
Freezing Level and BB
(170E-230E)
FL - BB
FL (30S-0, 0-30N)
10S-10N
BB
20S-20N
FL-BB
30S-30N
Comparison of rain estimates from
different algorithms (PR and TMI)
(Essentially the same as V6)
PR and TMI Regional Validation
TMI V6, PR V5
(W. Berg, et al.)
Summary
• TRMM PR uses three kinds of calibration methods.
– internal calibration
– external calibration with ARC
– calibration with natural targets
• PR's electric and electronic performance was
measured in the initial check-up period just after launch.
– absolute calibration error < 1dB
• All calibration methods indicate an extremely stable
performance of PR.
– HK data are all very stable
– overall long-term stability < 0.05dB
• The largest error in rain rate estimation probably
comes from the retrieval algorithms and not from the
radar calibration.
Acknowledgments
•
•
•
•
•
H. Hanado (JAXA)
N. Takahashi (NICT)
K. Okamoto (Osaka Prefecture University)
JAXA/EORC
and many other people who helped me.
Backup slides
External Calibration of DPR
flight
direction
PR and DPR calibration scan strategy
Rx
ARC
Rx
0.2°
0.1775° scan
(=1.25km) direction
Observed & retrieved 2D patterns by ARC
Improvement of angular resolution.
Multiple receivers (or ARCs) will
improve the along track resolution.
Variations in System Noise (TRMM PR)
frequency
• The system noise level is determined by
the thermal noise and the background
noise from the radiation of the earth
surface, precipitation, etc.
• The variation of the thermal noise is less
than 0.15 dB, and is stable for a long
period (Left Figure). The variation of the
background noise is also small (< 0.1 dB
over ocean, < 0.5 dB over land)
• The fading variation of the system noise
is about ±1 dB (Right Figure).
Long-term change of the system noise
and the solar beta angle (top), and the
FCIF temperature (bottom)
by Takahashi and Iguchi:IGARSS-2004
An example of the system noise distribution
(no-rain, over ocean, 100 orbits data)
Long term trend of (sampled) system noise
average for one orbit to remove the fading effect
-111.2
-111.3
0
Sun acquisition mode
FCIF temperature
20
0.8
0.6
16
0.4
14
12
100
200
300
Day from Dec. 1, 1999
TRMM implemented 180
deg. yaw manuevour
when the solar beta angle
reaches to zero.
-50
18
0
•
•
•
•
solar beta angle
50
0.2
400
STD of FCIF temperature
(2 orbits)
system noise (dBm)
-111.1
Good agreement with the FCIF temperature change
The temperature change is relating to the solar beta angle
The fluctuation of the system noise is about 0.15 dB
The system noise shifts by about 0.05 dB after the PR power off event
Changes in one orbit
-111.1
20
18
-111.2
16
beta <= 5
14
-111.3
0
6
12
18
FCIF temperature
system noise (dBm)
beta = 25-40
12
24
Local time (hr)
• Changes in the system noise when the satellite moves from the
sunny side to shadow side.
– The changes in system noise delays about 4 hours in local time (about 20
minutes in actual time)
– No clear dependency can be seen for low solar beta angles.
Differences in Rain Estimates
170E-230E
2A25
2A12
ERA-40
3B42
10S-10N
20S-20N
30S-30N
1998
1999
2000
2001
2002
Climate Variability
Models vs. Observations
Tropical Mean Rainfall Variability
Bias Adjusted Mean DJF Rainfall
(TRMM Retrievals)
Tropical Rainfall Anomalies
(Passive Microwave Algorithms)
Tropical Rainfall Anomalies
(TRMM Land Retrievals)
(Higashiuwatoko)
YYM M
00
00
00
00
00
00
99
99
99
99
99
99
98
98
98
98
98
98
11
09
07
05
03
01
11
09
07
05
03
01
11
09
07
05
03
01
(X - PR)/PR * 100 (%)
98
01
98
03
98
05
98
07
98
09
98
11
99
01
99
03
99
05
99
07
99
09
99
11
00
01
00
03
00
05
00
07
00
09
00
11
mm/hr
J. Kwiatkowski
V6 RP Ocean from L2 Zonals
0.13
0.12
0.11
0.1
0.09
0.08
0.07
0.06
PR
TMI
12
10
8
6
4
2
0
-2
-4
COMB
YYMM
V6 RP Ocean from L2 Zonals
(TMI-PR)/PR
(COMB-PR)/PR
(PR - PR)/PR
J. Kwiatkowski
0.13
0.125
0.12
0.115
0.11
0.105
0.1
0.095
0.09
0.085
0.08
PR
TMI
COMB
98
01
98
04
98
07
98
10
99
01
99
04
99
07
99
10
00
01
00
04
00
07
00
10
01
01
01
04
01
07
01
10
mm/hr
V6 Ocean from L2 Zonals +/-35deg.
YYMM
16
14
12
10
8
6
4
2
0
-2
-4
(TMI-PR)/PR
(COMB-PR)/PR
(PR - PR)/PR
98
01
98
03
98
05
98
07
98
09
98
11
99
01
99
03
99
05
99
07
99
09
99
11
00
01
00
03
00
05
00
07
00
09
00
11
01
01
01
03
01
05
01
07
01
09
01
11
(X - PR)/PR * 100 (%)
V6 Ocean from L2 Zonals +/- 35deg.
YYMM
Diurnal Variation of Rain from PR
Morning rain dominant
Afternoon rain (local time: 12-18 h)
Morning rain (local time: 6-12 h)
Afternoon rain dominant
-10
10
(March 1998 - February 1999)